Large area electronics aims to build electronic systems in large area format and at low cost. One of popular applications is flat panel displays that are widely deployed in consumer electronics. Large area imaging has also become an integral part of large area electronics where flat panel X-ray detector, optical fingerprint sensor, and biomedical fluorescent imaging are emerged. In large area imaging, pixel technology based on thin-film photodetectors and transistors is essential, enabling high sensitivity, high spatial and time resolution to address requirements of various applications. A conventional pixel usually consists of a photodetector such as photodiode or similar as a sensor and a thin-film transistor (TFT) as a readout switch in the passive pixel sensor (PPS) architecture. However, it suffers from low signal to noise ratio (SNR). To improve the SNR, an active pixel sensor (APS) including a photodetector and multiple TFTs was proposed by introducing in-pixel amplification. However, it trades off the spatial resolution as a result of planar integration where the photodetector and TFTs are kept separate laterally.

Therefore, advanced pixel technologies that have high SNR and high spatial resolution are on demand. In order to achieve both, a 3-D APS architecture is proposed where the photodetector is vertically integrated atop the TFT. In this talk, a few 3-D APSs based on amorphous silicon, low-temperature polycrystalline silicon, and spherical silicon material systems will be presented along with mechanisms that lead to high sensitivity and high spatial resolution.

State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University

Kai Wang is currently a full professor in the School of Electronics and Information Technology at Sun Yat-Sen University in China and also an adjunct professor in the Department of Electrical and Computer Engineering at Carnegie Mellon University in the US. He received his B.Sc. degree in Electrical Engineering from Huazhong University of Science & Technology, Wuhan, China in 2000, and M.A. Sc. degree in Microelectronics & Solid State Electronics from Dalian University of Technology, Dalian, China in 2003. He earned his Ph. D. degree in Electrical & Computer Engineering from the University of Waterloo, Waterloo, Canada in 2008 and was thereafter appointed as a NSERC postdoctoral fellow in Thunder Bay Health Science Centre，Thunder Bay, Canada where he had been conducting research on biomedical X-ray imaging until he joined Apple Inc. in Cupertino, California in August 2011. At Apple Inc., he was involved in touch sensor development for various Apple products such as iPad and Apple Watch.

His current research focuses on emerging applications of thin-film transistors including flat-panel X-ray imaging, fingerprint biometrics, tactile sensors, energy harvesting, sensor interfaces and etc. He has published over 70+ journal papers/conference proceedings and coauthored 20 patents (9 awarded). He had served as an Associate Editor of IEEE/OSA Journal of Display Technology from 2013 to 2016 and is an active member of IEEE, SPIE and SID.